# Find the direction cosines and direction angles of the vector ijk2i^+j^+2k^ - Mathematics and Statistics

Sum

Find the direction cosines and direction angles of the vector 2hat"i" + hat"j" + 2hat"k"

#### Solution

Let bar"a" = 2hat"i" + hat"j" + 2hat"k"

|bar"a"| = sqrt(2^2 + 1^2 + 2^2) = sqrt(4 + 1 + 4) = sqrt9 = 3

∴ unit vector along bar"a"

= hat"a" = bar"a"/|bar"a"| = (2hat"i" + hat"j" + 2hat"k")/3 = 2/3hat"i" + 1/3hat"j" + 2/3hat"k"

∴ its direction cosines are 2/3,1/3,2/3.

If α, β, γ are the direction angles, then cos α = 2/3, cos β = 1/3, cos γ = 2/3

∴ α = "cos"^-1(2/3), beta = "cos"^-1(1/3), gamma = "cos"^-1(2/3)

Hence, direction cosines are 2/3,1/3,2/3 and direction angles are "cos"^-1(2/3), beta = "cos"^-1(1/3), gamma = "cos"^-1(2/3)

Concept: Position Vector of a Point P(X, Y, Z) in Space
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